The long term objectives of this proposal are to understand the cellular and molecular mechanisms that underlie the capacity of the cerebral cortex to adapt to changes in patterns of input from the peripheral sense organs in adults. These mechanisms probably not only play a role in the fundamental processes involved in the learning of skills and the Capacity to make perceptive judgements about the external world but also appear to be involved in the aberrant perceptions that accompany perturbed peripheral sensory input, and in adaptation to central and peripheral nervous injury. The proposed studies, to be carried out in macaque monkeys, involve three principal sets of. experiments. The first set deals with how converging and diverging connections extending from the -thalamus to the somatosensory cortex may facilitate plasticity of representations of the body, but -place constraints upon the extent to which changes can occur. The second set of experiments deals with the issue of whether pre-existing connections within the somatosensory cortex itself are sufficient to permit large scale changes in representational maps after long-term deafferentation or whether it is necessary for new connections to be formed. This set introduces a new model for the studies of cortical plasticity, the face representation, and addresses the issue of whether it is protected" from other parts of the somatosensory cortex by an absence of interconnections. The third set of experiments deals with the normal patterns of gene expression for receptor subunits and other polypeptides that form components of the inhibitory (GABAergic) and excitatory (glutamergic) transmitter systems of the cerebral cortex and thalamus and asks to what extent activity-dependent changes in gene expression for these molecules accompany and/or contribute to representational plasticity. The methods are a combination of anatomical tracing, physiological mapping in normal animals and in animals in which part of the thalamic representation has been selectively lesioned, coupled with immunocytochemistry and in situ hybridization histochemistry, and including a search for novel GABA-A receptor subunit genes.